Vitamin D deficiency is widespread in newborn. Streym and colleagues analyzed cord blood from 107 Caucasian women and their infants at birth, 4 and 9 months living in Denmark. Serum 25(OH)D levels < 25 mmol/L and between 25-50 nmol/L were defined as deficient and insufficient, respectively. Plasma 25(OH)D levels were higher in women using supplements (79 vs 53 nmol/L) and 23% of women were insufficient. As the study progressed, fewer women were using dietary supplements and plasma 25(OH)D levels decreased. There was a positive correlation between maternal plasma 25(OH)D and cord blood concentrations. At birth, 15% of infants were deficient and 46% were insufficient. Plasma 25(OH)D levels were lower during winter. Maternal plasma 25(OH)D level was the only significant determinant of infant vitamin D status at birth and visit 2 whereas season was also important at 9 mo. Based on widespread vitamin D deficiency in newborn Danish children, the authors recommend vitamin D supplementation daily for infants (400 IU).

A similar story can be told for adults. Caillet and colleagues examined reimbursement data from 1,311 middle-aged French adults who had been prescribed vitamin D supplementation based on serum 25(OH)D levels. Physicians prescribed a very high dose (100,000 or 200,000 IU) in 32.6% of patients. Only 51% of patients received further vitamin D supplementation after a single loading dose. The most common daily vitamin D dose over the 7 month followup was <1000 IU (~47%) followed by 1000-2000 IU (~30%) with a median of 1,600 IU/day.

Be prudent. If you live in the southern hemisphere, go outside and enjoy some sunshine. If you live in the northern hemisphere (or prefer not to spend time in the sun), a vitamin D supplement is smart.